1. Field of the Invention
The present invention relates to a mobile communication terminal, and particularly to an apparatus for controlling power of a mobile communication terminal.
2. Description of the Background Art
In a terminal of a mobile communication system, an internal temperature of the terminal has large influence on its performance and used hours of a battery. Because of this, the terminal includes a temperature detecting device and an amplifying device therein, and thus can check the internal temperature of the terminal, and adjust transmission power according to the temperature, through these devices.
FIG. 1 is a block diagram of a transmission apparatus of a general mobile communication terminal.
As shown therein, the general mobile communication terminal includes a modem 110 for outputting an intermediate frequency (IF) signal and an auto gain control (AGC) signal; a gain controller 120 for adjusting a gain of the IF signal outputted from the modem 110, according to the AGC signal; a frequency mixer 130 converting the adjusted IF signal into a radio frequency (RF) signal; a drive amplifier 140 for amplifying the RF signal; a filter 150 for bandwidth filtering the amplified RF signal; a power amplifier 160 for sufficiently amplifying power of an output signal of the filter 150 as much as the output signal can be transmitted to a receiving side through the air; and a thermistor 170 for detecting an internal temperature of the terminal and applying the detecting result to the modem 110.
For convenience sake of explanation, hereinafter, the frequency mixer 130, the drive amplifier 150, and a power amplifier 160 will be referred to a transmission signal processing block.
In the background art constructed as above, the thermistor 170 receives a predetermined voltage corresponding to the internal temperature of the terminal, converting the received voltage into a DC voltage, and applying the DC voltage to the modem 110. Then, the modem 110 estimates an internal temperature of the terminal based on a level of the applied DC voltage, and compares the estimated temperature with a reference temperature. Through this comparison, the modem 110 generates a predetermined AGC signal so that the terminal can maintain a proper temperature thereof, and applies the AGC signal to the gain controller 120.
The gain controller 120 adjusts power of the IF signal outputted from the modem 110, according to the applied AGC signal.
Through the process above, the mobile communication terminal controls the gain of the transmission power so as to prevent its internal temperature from increasing more than the reference temperature. In the background art above, considering that characteristics of internal devices of the terminal is changed according to a temperature, the thermistor 170 is mounted in the vicinity of internal devices of the terminal. In addition, using the thermistor 170, the internal temperature of the terminal is compensated.
However, since the thermistor is implemented as an independent circuit and the internal temperature of the terminal is affected by various environmental factors, the temperature detected by the thermistor does not always correspond to actual power of the transmission apparatus.
That is, since a resistance characteristic value of the thermistor is changed according to change of the internal temperature of the terminal and thereby changing the DC voltage level, a compensation value which actually controls power, may not be correct. If power is outputted more than a reference level by incorrect compensation, a battery is rapidly consumed.